The present invention concerns a radial shaft seal comprising a gasket and anti-dust lip made of polymer and resting axially separated against the shaft and with continuous sealing edges around it.
Such a radial shaft seal is known from the published German patent application No. 1,284,203. Its tightness derives from a fluid being constantly supplied to the space being sealed from below the sealing edge as the shaft rotates. To prevent a vacuum between the sealing lip and the anti-dust lip that would force them too strongly against the surface of the rotating shaft, the space between the lips communicates through a vent with the space being sealed off. It must of course be taken into account that the fluid being sealed out, lubricating oil for example, can penetrate through the vent into the space between the lips, and leak out past the anti-dust lip while the shaft is not rotating. The result is more dust outside the anti-dust lip, which not only looks bad, but also increases wear on the lip as the shaft begins to rotate again.